rockkid777 / Todo

Example app for a Docker introduction in dev environments

Todo

A minimal project showcasing usage of Docker and Docker Compose tool for local service development.

This document is a live document evolving through Docker introduction sessions.

Next Steps

• Fix entrypoint issue in Dockerfile
  • Solve it for the current project
  • Provide a more generic solution, a more portable Dockerfile
• Environment variable handling
  • separate configuration for containerized environment
• Volume handling
• Dependencies between services
  • What is it good for and what is it not

Previously on Docker introduction

First session

• Tech requirements
  • Docker for desktop (or any other Docker installation)
  • Todo project repository
  • Dotnet Core (Optional, for the local setup tryout)
• Minimal intro to Dotnet Core MVC app project
  • dotnet run - build and run (see --help for details)
  • dotnet publish - build and package (see --help for details)
  • appsetings.json and appsettings..json - configuration files with connection strings
• Running a PostgreSQL instance in docker
  • PostgreSQL docker image (and documentation) in library
  • Injecting environment variable
  • Expose PostgreSQL server to localhost on 5432
• Running Todo app connecting to PostgreSQL
  • Adjust connection string
  • dotnet run --project Todo.csproj
• Create Dockerfile
  • Dockerfile reference
  • Multistage build, with build-env stage and final stage
  • Creating .dockerignore to exclude local bin and obj folders
  • Build image with docker build -t 'todo:0.1' .
• Creating docker-compose.yaml for project
  • docker-compose reference
  • webapp service
    • build context is the current project folder
    • bind localhost:9090 to port 80 of the container
  • db service
    • specify image 'postgre'
    • specify db password as environment variable
• Start up project
  • docker-compose up
  • docker-compose build needed on code change to rebuild webapp image
  • webapp container fails on start logging application error

Questions and Answers

• How much my application coupled to docker? Can I 100% decouple it from docker? I mean later on I may want to use a different container.
  • Docker-Compose what we're using here for project-environment setup is coupled with Docker, directly using it's API.
  • The webapp itslef is not coupled to Docker. The Docker image being built is an OCI standard container image, which basically a filesystem image with some meta labels telling how the author intended their image to run.
  • Docker container runtime is a OCI standard container runtime. Does not really differs from jails (BSD) or chroot (linux) which runs a process defining what resources it can access and how, providing a virtual environment (process level virtualization).
  • Alternatively, OCI standard container images can be built with e.g.: Jib (Java specific), OCI standard container runtimes: rkt and runc